I'm an immigrant Mom in the US. Moved here to marry in the 80's
Most of the time I have really loved living here, I have had good friends and a good job (sahm now) But the last few years, the distance from family has got to me, my mother has become widowed, my father and step father died within weeks of each other and I have a strong need to go home to help her and be near as she gets older (she's 71) My oldest has moved there and is working, he lives with grandma so I have an eye on her. Next Spring the second son will move there too. Then it's time Dh and I got up and moved with Dd. (we are all dual nationals so no visas needed)
Biggest gripes in the US.
Lack of paid vacation time compared to UK.
Worries about health care paying for it, and having it tied to a job, so you feel trapped with in that job. The cover you buy between jobs is more than our mortgage payment
Other than that it's what you make of it, same as anywhere else.
It is however a foreign country with it's own rules regulations and customs, no matter what any one tries to tell you. I still feel like a foreigner after all there years.